The Stovebolt Site Forums The Parking Lot Big Bolts BRAKES ON A 1953 6400

I haven't been here for a long time. Several years ago I restored a 53, 6400. I don't know how I would have managed without this site. I got it 99 percent finished and more or less lost interest in it. It was done with the exception of some smaller cosmetic issues, and by that time I was tired of it. One problem I have had from the beginning is the brakes. I thought that would be the easiest part of the whole process, but I have never been able to get them right. I will get them up, with a good hard pedal, and lots of brakes. I will drive it a little,let it sit for a while, and when I come back the brakes are gone, or nearly so. The more I drive it, the worse it gets. It takes almost nothing to bleed them. I will go to the back left real wheel, run a little fluid through the bleeder valve, and be fine again for a short while.

I have done everything I can think of with no success. Today, I decided to take the master cylinder off and look at it. I didn't know what I was looking for, but I thought I might get lucky, and see something that seemed out of line. As you might expect, everything seemed ok, I put it back together, and now I can't get the fluid to go out of the master cylinder to the brake lines. I don't know what I have done wrong, but I must have put something back together wrong. There aren't that many parts, so I can't imagine what I have done. I have a shop manual, but it doesn't give a good picture of the way the cylinder should be assembled. Question: I think both the large rubber cups point in the same direction. One of them can go only one way because it is fastened to the piston. I think the other one points in the same direction. Is that correct? That is the way I have put it together. I have had the master cylinder apart before, and never had this problem. It has been a while, and my memory might be playing tricks on me.
I'm about ready to set the whole thing on fire and forget it. Can anyone help? Thanks, Bakerallen

Bakerallen,

Is there a hydrovac unit in your brake system?

Tim

Hy Bakerallen, did you "bench bleed" the master before you re-installed it?

One possibility is that your residual pressure valve in your master cylinder might have been leaking. When that happens, it allows the wheel cylinders to ingest air past the wheel cylinder cups. As for the master, yes, I believe that the flared end of both cups goes toward the outlet of the cylinder. Here's an exploded diagram:

http://chevy.oldcarmanualproject.com/gmc/5559mm/5559mm175.html

Thanks for the quick replys. This is absolutely the worlds best site. Yes I have a Hydrovac, No I didn't bench bleed the master cylinder this time. I have not been working on the truck for a long time, and I forgot to do that, but I have done it in the past. 1herrick1. I actually think you may have the answer. I more or less came to the same conclusion, but I didn't know what to do about it. I'm not losing any fluid, except for a very small weep at one of the fittings. It doesn't take much to get the brakes going again, once I bleed them at the back wheel. This makes me think I must not have a problem with air in the lines, which leads me to believe the pressure on the lines must be drifting back to the master cylinder. If that is correct, what to I do about it. Will a new master cylinder kit fix the problem?? And why can't I now get the fluid to leave the master cylinder and pump out to the lines?? Thanks Allen

Don't give up, did my brakes and was not happy with the way they felt. I put a new master cylinder on and new wheel cylinders all around. I need to rebuild my Hydrovac, but , bypassed it for the time being till money comes available. Being that I am only 15 minutes away from John and Peg, I got John to come up and help me with bleeding mine. I first adjusted my brake shoes to the point to where they were almost dragging and then we bled the brakes. I did not like the feel of them for a long time ,but, they have actually gotten better with time. Also blew my lines out with brakeclean before installing my wheel cylinders and replaced with Dot-5 silicone brake fluid. I was urged to spend the extra money and do so because of the reliability of it.

If you didn't bench bleed the master, then you've got a bit of a problem. It's very difficult to bleed one properly with it connected to the system. Not to mention the fact that you've now likely pumped the lines full of air. And yes, the best way to cure a residual pressure valve problem is to rebuild the master again with a fresh, new kit. Start with that, repair any leaks in the system, and rebleed the whole system from scratch. When you're bleeding, make SURE that you don't run the master dry or else you'll have to bench bleed the master all over again. About three good pumps is about all you can safely get before it'll need topped off. I know the brake hydraulics are a pain. I just bled mine the day before yesterday after working on the system on and off for 18 months. A little air anywhere in the system will cause pressure problems. It just takes patience! Here's a link to the proper bleeding sequence:

http://chevy.oldcarmanualproject.com/gmc/5559mm/5559mm172.html

The best was to ensure no air in the system is to power bleed them. The master and the cylinders are at about the same level so it's hard to get the air to move by pumping the pedal. Once you use one, you'll never go back,
Scott

Are you following the bleeding procedure in the Shop Manual. In particular, the procedure for bleeding the hydrovac unit (before bleeding the wheel cylinders)?

http://chevy.oldcarmanualproject.com/shop/1954truck/54ctsm0527.html

I would guess that your 1953 should be bled as described for a '54 Chevrolet truck with a hydrovac unit.

The procedure described in the GMC maintenance Manual is slightly different, but the hydrovac unit is also bled first.

again, thanks: As I said earlier, I didn't bench bleed the master cylinder this time, because I forgot about that. But at one time or another, with the exception of power bleeding, I've done all the things suggested above, and I still start out with lots of good hard pedal and then it goes away as I drive the truck. It's not a matter of the brakes not being quite right. In the beginning, they will be fine, and then gradually get worse and worse until there is nothing left. This time is different in that for some reason I can't get the fluid to pump out of the master cylinder. That's new. I think my next move is to put a new kit in the master cylinder. Does anyone have any suggestions where I might find one? Thanks Allen

One thing that could be an issues is if you have a faulty seal inside of the Hydrovac. There should be a plug on the back of the power piston cannister where a very small amount of fluid is added to lubricate the power piston. If you pull that plug and brake fluid comes out, youll know what the problem is and why its fine for a little while and then gets squishy as time rolls on since its slowly leaking past a seal every time the brakes are pushed.

Theres a long list of vendors under the links section at the top of the page. A few good ones being Jim Carters, The Filling Station, Chevs of the 40s, etc.

Good luck! Jeff

This thing is driving me crazy. I can't get the master cylinder to pump fluid out of the top reserve chamber. The little holes are open. I checked that. The piston seems to be hanging up. When I have it off the truck, I can push the cups and the piston toward the push rod, but then it is very hard to push them the other way using the rod. All the parts look fine and the cylinder is perfectly smooth. Has anyone ever run into anything like this before? I keep thinking I must be putting it together wrong, but It's so simple, I don't see how that's possible. Various suppliers have master cylinder kits, but they come in different sizes, and I don't have any way to accurately measure the inside of the cylinder. Does anyone know what size I need?

If its a stock master, usually it has the number stamped on the side of it. Otherwise my best guess would be 1 1/4", but remember thats a guess!

Thanks for the info. There is a number on the outside of the cylinder, but it looks like a serial number or something. However in taking it apart again, I noticed that one of the rubber cups is marked 1 1/4. Also I managed to get a micrometer inside far enough to get what I think is an accurate reading. It also said 1 1/4. I just ordered a repair kit from Jim Carter. Using a light on the outside and a very fine wire, it looks to me as if the front rubber cup is not clearing the very small hole that lets fluid down into the body of the cylinder. When I have the cylinder in a vice it will work, but there is no pressure on it. I think possibly on the truck there is enough back pressure to cause the cup to close the hole off.

On a different subject: In the shop manual there is a picture of a hydrovac that shows what looks like a plug to put brake fluid to lubricate it. Also the manual calls for that to be done. Someone on this site also said that was correct. However, the unit I have does not have the plug. Seem strange, but there is no plug. This is a unit that I bought when I was rebuilding the truck, and supposedly it had been rebuilt. I think it came from NAPA, but I'm not sure. I started to take it apart one time, but didn't have wrenches large enough, and didn't get that done. I did get the vacuum tank off and that had a lot of dirt in it. Leads me to think someone may have given it a coat of fresh paint and called that rebuilding. Is there another way to lubricate then inside of the unit? Thanks Allen

Is it the older style of Bendix Hydrovac, looks like a coffee can with 4 J-bolts, or a Midland type Hydrovac, looks almost like what a newer truck might have.

This is what a later model Bendix or an early model Midland booster looks like.

This is what the older Bendix models look like.

I believe the Midland types are supposed to be a sealed assembly with no way to add fluid but im not positive.

Jeff

mine is the older bendix. After I get the master cylinder repair kit from Jim Carter, and IF that works, and I still have problems, I'm going to do something about the hydrovac. In one of the online catalogs I saw someone had a rebuilt one for almost $600.00. That's a big plate of not gonna happen. If I can't repair it, I going to disconnect it, and forget about it. I don't really need it. I'm not likely to put 5 tons on the old truck and go anywhere. Plain old brakes should stop anything I would put on it. Do you know anything about repairing a unit like I have? Is it a big deal, and are parts available. Again, thanks for your help. I do appreciate all the effort you are making to help. Allen

Heres the tech tip I wrote on overhauling them.

I spent $50 through ABS for my kit but it did not come with the control valve diaphragm or the large power piston seal. I already had a control valve diaphragm, but the old one still looked fine with no degredation. The power piston seal was originally a leather seal, but newer ones had rubber and rope seals and those hold up really well. I know you can also get the parts through BSC but you have to argue with them to get a kit. They dont like to sell kits, probably because they make more money with a trade in or a rebuild. A fully stocked kit will run around $100.

I dont know what to do about adding fluid to the power piston cannister since yours doesnt have a plug. Id probably pull the casing off and add about two ounces of mineral oil, no more. You DO NOT want to use any lubricant that is petroleum based. A thin synthetic (corn based or other) oil would work also.

Hope that helps. If not keep firing questions off!

Jeff

Why are you going mail order? My CarQuest has most of that stuff on the shelf or in town the next day. They had a set of front shoes, grease seals and a master cylinder for me the same day,
Scott

Scott,
I have not had that kind of luck with NAPA around here (BC) or Washington State. They can't even find stuff in the books let alone order it. I find it very convenient to use Jim Carter. At least I know they have it.
I remember when I lived in Lexington, KY there was a parts store that would have any part just about by 5 if you went before noon. I think it was called Eastland Auto Parts.

Jeff: Thanks for the information on rebuilding the hydrovac. I haven't gone through it yet, but I fully intend to do that. It looks as if you put a lot of time into putting it together.
Scott: It depends on the store, and the clerk as to the service you get, and the parts available. Unless you have a retailer who is interested in doing more than just taking orders you are not going to get much out of a Carquest, or NAPA, or any of the other regular auto parts stores. For example: I know NAPA can get a lot of parts for these older vechicles, but most parts clerks either don't know how to find them, or don't care enough to look. I have had some luck with finding rebuilt parts from NAPA, but I have also been told at other stores they can't help me, with the same part. I agree with Shop Shark. It's easier to deal with some one like Jim Carter, who does care about their business, and won't get belligerent when you take him off the phone with his girl friend.

There are still companies that have been around that have been rebuilding them for a long time. San Antonio Brake and Clutch in San Antonio still does it. Most larger cities still have someone who rebuilds them.

I had one rebuilt recently for around $300. Let me know if you want contact information.

My experience with Napa has been the same, with an exception that if they cannot find it in the computer they wont even try to look for it. Half the time they get pissy when I bring them a part number. I just spoke wih a guy yesterday who told me to look elsewhere since he didnt want to try. Dipshits...

We used to have a Westbay auto parts which was great. It was a dirty store but they liked a challenge and would dig through books to try and find what you needed. Recently they signed on with Napa and if you get one of the Napa folks you may as well give up. There are still a few old Westbay guys working there that arent afraid to get their hands dirty, but so far Im unimpressed with Napa.

The only other store in my area is Schmucks and they are worse unless your looking for something built within the past 15 years...

tcledermans rave reviews over Rockauto got me to start shopping there. They have great prices and even ordering the wrong or a bad part theyve made good on a replacement. I cant say enough good stuff about them.

rustednuts,

Do you have a part number for a hydrovac that can be found on Rockauto.com.

Unfortunately, Rockauto.com does not show large trucks in their catalog search; however, they allow a search by brand and part number - I've found a lot of parts that way.

Tim

Nope, sorry Tim. I had to send in my seals out of my Hydrovac so that they could check the sizes and get me the appropriate kit since they came in so many different sizes and shapes, and mine had no identification tag. Im always looking for new places to find seals and parts for old vehicles but I havent tried searching Rockauto just yet for brake components.

Tim, when you do a search for parts what do you do if you do not know the brand of manufacture? Ive tried searching part numbers to no avail, but if I add the correct manufacturer it pulls up the parts. Am I missing something?

Thanks, Jeff

Jeff,

Yes, you need to know the manufacturer and that manufacturer's part number for the Rockauto.com cross-referencing to work.

Unfortunately, knowing the GM, Chevrolet, or GMC part number does not help, either.

Tim

Haven't been here for a while. Been busy and haven't time to work on the truck. I ordered a new kit for the master cylinder from Jim Carter. Put it in a few days ago, and have driven the truck a little. It seems to be working, but I won't be sure until I drive it more. In the past, I would get the brakes up, and then as I drove it, they would gradually go away. That doesn't seen to be going on this time, but I can't be sure just yet. I don't understand it. The parts I put in look just like the ones I took out. The ones I replaced were new when the truck was rebuilt and it has been driven very little since then. One of lifes mysteries I guess. I can't tell if the hydrovac is working or not. I have been told you can hear them working as the the brakes are applied and released. I don't hear anything, but the brakes seem fine. It doesn't take a lot of pressure to make them work. Thanks to everyone for their help and concern. Allen